Electrical end switches for use in machine tools



Jan. 3, 1967 H. R. SCOTT 3,296,392

ELECTRICAL END SWITCHES FOR USE IN MACHINE TOOLS Filed Dec. 1. 1964 2 Sheets-Sheet l Jan. 3, 1967 H. R. SCOTT 3,296,392

ELECTRICAL END SWITCHES FOR USE IN MACHINE TOOLS Filed D90. 1, 1964 2 Sheets-Sheet 2 United States Patent 3,296,392 ELECTRICAL END SWITCHES FOR USE IN MACHINE TOOLS Harold Richard Scott, London, England, assignor to Birmingham Small Arms Limited, Birmingham, England, a British company Filed Dec. 1, 1964, Ser. No. 415,044 Claims priority, application Great Britain, Dec. 6, 1963, 48,264/ 63 Claims. (Cl. 20047) This invention relates to electrical end or limit switches for use in machines such as machine tools and has for an object to provide an improved end switch premits failure in the mechanical part of the switch to be remedied without the need of undoing and re-establishing electric wire connections.

In the case of machine tools and other machines in which electrical end switches are employed to terminate or reverse the direction of the movement of a machine part, failure of such end switch renders the whole machine unfit for use. The failure thus not only ties up, until repair can be effected, the considerable capital invested in the machine but is, for example in the case of machine tools, also liable to interrupt production on other machine tools performing other machining operations on the same part, and possibly a whole complex production line in which the part is required. It is therefore important for such end switch to be so constructed as to enable the machine to be restored to full operation with as little delay as possible. With this object in view it has previously been proposed to provide the end switch with a pin-contact base having contact pins which co-operate with socket contacts secured in the machine frame or other part of the machine tool and attached to wiring provided in the latter. This construction may be called a pin-base switch and has the advantage that in the case of breakdown of any switch it is only necessaryprovided that a replacement switch is available-to withdraw the original switch from the socket contacts and to insert in its place the replacement switch. The arrangement has however the disadvantage of introducing a plug-and-socket contact connection into each lead requiring connection to the switch. Such a con nection increases line resistance and decreases reliability, more particularly in the case of circuits working at comparatively low voltages, and it is therefore a more specific object of the present invention to provide an improved end switch for use in machine tools and other machineswhich, while offering most, if not all, the advantages of the pin-base switches, does not require the introduction of additional contact connections.

According to the present invention the switch has a housing made in two parts, one of which is intended for permanent attachment to the machine and contains the fixed contacts of the switch, to which external connection leads may remain permanently attached, while the other part is detachably mounted on this first part and contains the operating mechanism including the movable contacts, the switch being so constructed that the movable contacts are only employed to establish connections between fixed contacts contained in the firstmentioned part and do not have to be themselves attached to any wiring. Preferably the fixed contacts are all set back from the face of the first part of the switch housing so that all potentially live parts are out of accidental reach, while the movable contact or contacts is or are carried by a member or members arranged in the second part of the housing, from which they project in cantilever fashion. The second part of the housing with the switch mechanism and movable contacts carried by it constitutes a replaceable unit and replacement units con- 3,296,392 Patented Jan. 3, 1967 stituting this combination can be kept available for use in a machine in case of failure of any switch. Protection of the replacement unit and its contacts from accidental damage can, according to a further feature of the invention, be achieved by providing a cap adapted for attachment to the replacement unit in lieu of a first-part housing member, the cap being constructed to accommodate all those elements of the replacement unit which project beyond the attachement surface of the latter. Conveniently this cap forms a dummy housing equipped with abutment surfaces corresponding to the fixed contacts of the first part of the housing, so that, when a replacement unit is attached to such cap member, the operation of the switch mechanism of the unit can be tested. In order to allow this operation to be visually checked, the cap member may conveniently be made of transparent plastic. The abutment surfaces of the cap member may, if desired, be equipped with test contacts having suitable external connections. This facilitates electrical testing in addition to mechanical testing of the replacement unit. The accompanying drawings illustrate one switch according to the present invention.

FIGURES l is a sectional elevation of the switch, and FIGURES 2 and 3 are respectively plan views of the replaceable unit and of the fixed part of the switch.

Referring now to the drawings, the switch has a housing formed in two parts 1, 2, each of the form of a box which is open at the face 29 or 29a adjoining the other part. The former part can be permanently secured to a suitable part of a machine tool or other machine, for example by screws extending through bores 3 and 4. This housing part contains an insulating block made in two portions 5 and 5a. The former portion extends close to the surface 29, and both portions are secured to the housing 1 by screws 6. The insulating block carries two pairs of fixed contacts 7, 7a and 8, 8a, these contacts being set back from the surface 29 and being respectively connected electrically to terminal screws 17, 17a and 18, 18a. The other housing part 2 is secured to the fixed housing part 1 by screws 9 which engage threaded bores 10 in the wall of housing part 1, accurate relative location of the two parts being ensured by bosses 11 of housing part 1 which engage corresponding recesses in the housing part 2. When a replacement unit is substituted for the replaceable unit including the housing part 2, the replacement unit will therefore be accurately located in relation to the fixed housing part 1. Supported by a bearing 12 in the detachable housing part 2 is a switch-actuating shaft 13 extending at right angles to the surface 29a. This shaft is equipped outside the housing with an operating lever 14 and is, inside the housing, coupled by springs 15, 16 with an actuating arm 22 and a biasing plate 23 respectively. The actuating arm 22 operates, with a snap action ensured by a cocking spring 26 and triggered latches 27, 28, a contact-carrier arm 19, and the latter is pivotally supported on a pin 24, and is equipped with an insulating member 20 in which a contact bar 21 is supported for free pivotal movement about an axis extending radially of the pivot pin 24. It will thus be seen that the contact bar 21 will interconnect, in one end position of the contact-carrier arm 19, the fixed contacts 7 and 7a and in its other end position the fixed contacts 8 and 8a, provided in the housing 1. It will also be observed that the contact carrier arm 19, projects with its contact carrier member 20 beyond the surface 29a of the detachable housing portion 2. The member 20 and contact bar 21 therefore project into the opening of the fixed housing portion 1 for engagement with the contacts 7, 7a, and 8, 8a. Preferably a plate 30, having apertures 31 for the passage of the carrier arm 19, is arranged on the detachable housing part 2, approximately flush with the surface 29.

When a switch according to the invention becomes defective, for example due to breakage of one of its springs or to mechanical wear, its replaceable unit, which includes the whole of the switch-actuating mechanism, can be readily exchanged against a replacement unit by merely removing the two attachment screws 9, by which then the replacement unit is fixed in place of the defective unit. In order to avoid damage to the replacement unit during transport, each replacement unit is preferably protected by the attachement of a cap, which may conveniently consist of transparent insulating material. This cap may be somewhat similar in shape to the fixed housing member 1 and similarly equipped with screw threads 10 and locating bosses 11 and it preferably has a cavity in which the contact-holder arm 19 with members 20 and 21 can move within the range of switch operation. Abutment surfaces located similarly to the fixed contacts 7, 7a and 8, 8a are preferably provided in the cap to limit the movement of the contact bar 21 similarly as its movement is limited when the replacement unit has been incorporated in a complete switch. The fixed housing part 1 as shown has in one of its side walls a screwthreaded wiring aperture 25 through which electrical wiring connections can be introduced for attachment to screw terminals 17, 17a and 18, 18a. The attachment of the wiring elements to these terminals may be eifected when the insulating block 5, a is already in position in the fixed housing part 1 or previous to its insertion; in the latter case the attachment may be effected while the two portions 5 and 5a of the insulating block are still separate from each other.

What I claim is:

1. A switching unit, comprising a housing member formed by a circumerential wall defining a cavity and a top wall closing said cavity at one edge of the circumferential wall, the other edge of the circumferential wall defining an attachment surface, locating means adapted to prevent displacement of the housing along said attachment surface, a switch-arm member mounted in said housing for pivotal movement about an axis perpendicular to said attachement surface, but prevented from movement in the direction of said axis relative to the housing member, an actuator shaft mounted in. said housing member for pivotal movement about an axis parallel to and laterally displaced from the pivot axis of said switch-arm member, said actuator shaft extending through said top wall of the housing member, means re-. taining said actuator shaft against axial displacement relative to the housing member, and snap-action transmission means accommodated in the housing member and interconnecting the actuator shaft and switch-arm member to produce snap-action pivotal movement of the switch-arm member from one position to another position and vice versa when the actuator shaft is respectively turned in one direction from a first position to a second position and turned back from said second position to a first position by rotation in the opposite direction, said switch-arm member having a cantilever extension projecting from the housing member beyond said attachment surface, said extension having at least one contact surface arranged wholly at the outer side of said attachment surface and being spaced radially from the pivot axis of the switch-arm member.

2. A limit switch for use in a machine, which comprises a first housing part having at one side an opening surrounded by a fiat surface, and having mounting means for attachment to a machine with said opening freely accessible, a plurality of first contacts each having a contact surface, mounted in said housing part with said contact surface accessible through said opening along a line perpendicular to said surface, at least some of said first contacts having wire-attachment means, a second housing part detachably mounted on said fiat surface of the first housing part to cover said opening thereof, a switch-arm member wholly supported in said second hous ing part for pivotal movement about an axis perpendicular to said flat surface, and actuating means, including an element arranged outside the housing, for the switcharm member, said switch-arm member extending through said opening into the first housing part and including at least one contact, arranged at the outer side of said surface relative to said first housing part and radially spaced from the pivot axis of said arm, for co-operation with said first contacts to form, when the arm is in the first pivotal position, a connection between at least two of said first contacts, and to remove said connection when the arm is in a second pivotal position.

3. A switching unit as claimed in claim 1, wherein the actuator shaft, the switch-arm member except for said extension, and said snap-action transmission means are wholly arranged at one side of said attachment surface.

4. A switching unit as claimed in claim 1, further including a cover plate arranged approximately flush with the attachment surface to close said cavity at the said other edge of the circumferential wall, said cover plate having an aperture through which said extension passes.

5. A limit switch as claimed in claim 2, including an insulating body secured in the first housing part and having a portion near said flat surface, said first contact being so supported by said insulating body as to be further removed from said attachement surface than is said portion of the insulating body.

References Cited by the Examiner UNITED STATES PATENTS 2,459,077 1/ 1949 Jeffrey ZOO- 2,761,030 8/1956 Jeffrey 2 0O70 2,807,685 9/1957 Jeffrey 20070 2,856,068 10/1958 Paige 206-46 X 3,068,332 11/1962 Jeffrey 20047 X BERNARD A. GILHEANY, Primary Examiner.

T. MACBLAIN, H. SPRINGBORN, Assistant Examiners. 

2. A LIMIT SWITCH FOR USE IN A MACHINE, WHICH COMPRISES A FIRST HOUSING PART HAVING AT ONE SIDE AN OPENING SURROUNDED BY A FLAT SURFACE, AND HAVING MOUNTING MEANS FOR ATTACHMENT TO A MACHINE WITH SAID OPENING FREELY ACCESSIBLE, A PLURALITY OF FIRST CONTACTS EACH HAVING A CONTACT SURFACE, MOUNTED IN SAID HOUSING PART WITH SAID CONTACT SURFACE ACCESSIBLE THROUGH SAID OPENING ALONG A LINE PERPENDICULAR TO SAID SURFACE, AT LEAST SOME OF SAID FIRST CONTACTS HAVING WIRE-ATTACHMENT MEANS, A SECOND HOUSING PART DETACHABLY MOUNTED ON SAID FLAT SURFACE OF THE FIRST HOUSING PART TO COVER SAID OPENING THEREOF, A SWITCH-ARM MEMBER WHOLLY SUPPORTED IN SAID SECOND HOUSING PART FOR PIVOTAL MOVEMENT ABOUT AN AXIS PERPENDICULAR TO SAID FLAT SURFACE, AND ACTUATING MEANS, INCLUDING AN ELEMENT ARRANGED OUTSIDE THE HOUSING, FOR THE SWITCHARM MEMBER, SAID SWITCH-ARM MEMBER EXTENDING THROUGH SAID OPENING INTO THE FIRST HOUSING PART AND INCLUDING AT LEAST ONE CONTACT, ARRANGED AT THE OUTER SIDE OF SAID SURFACE RELATIVE TO SAID FIRST HOUSING PART AND RADIALLY SPACED FROM THE PIVOT AXIS OF SAID ARM, FOR CO-OPERATION WITH SAID FIRST CONTACTS TO FORM, WHEN THE ARM IS IN THE FIRST PIVOTAL POSITION, A CONNECTION BETWEEN AT LEAST TWO OF SAID FIRST CONTACTS, AND TO REMOVE SAID CONNECTION WHEN THE ARM IS IN A SECOND PIVOTAL POSITION. 